Circuit Board and Method for Producing Circuit Board

This application claims the benefit of priority to Japanese Patent Application No. 2023-069294 filed on Apr. 20, 2023 and is a Continuation Application of PCT Application No. PCT/JP2024/014333 filed on Apr. 9, 2024. The entire contents of each application are hereby incorporated herein by reference.

The present invention relates to circuit boards and methods for producing circuit boards.

WO 2022/202322 A discloses a line board including an insulating layer and a conductor layer formed on one main surface of the insulating layer, in which the insulating layer has a hole with the conductor layer as a bottom and opened toward the other main surface of the insulating layer, a first via portion connected to the conductor layer and a second via portion connected to the first via portion are provided in the hole, the first via portion includes a conductive member and does not include a resin member, the first via portion has a protruding portion in which an end surface of the first via portion on a side of the second via portion protrudes toward the second via portion, a portion of the second via portion extends to between the protruding portion of the first via portion and the insulating layer, and is not in contact with the conductor layer connected to the first via portion.

WO 2022/202322 A describes that an interlayer connection conductor including a first via portion and a second via portion is formed by forming a first via portion partway through a hole by plating a hole provided in an insulating layer with conductor foil, and then forming a second via portion by filling a remaining portion of the hole in which the first via portion is formed with a conductive paste.

Further, WO 2022/202322 A describes that insulating layers including an insulating layer with conductor foil in which a first via portion and a second via portion are formed are sequentially stacked, and then the obtained stack is heat-pressed (collectively pressed) in a stacking direction to prepare a stacked substrate (hereinafter, also referred to as a multilayer circuit board).

In general, a surface of a conductor foil such as a Cu foil is subjected to rustproof treatment. By forming the rustproof layer on the surface of the conductor foil, oxidation of the conductor foil can be prevented, and inhibition of adhesion to the insulating layer can be reduced or prevented. On the other hand, the reaction between the conductive paste and the conductor foil is reduced or prevented by the rustproof layer, so that connection reliability between the interlayer connection conductor including the first via portion and the second via portion and the conductor layer may be deteriorated.

Example embodiments of the present invention provide circuit boards each with excellent connection reliability between an interlayer connection conductor and a conductor layer, and methods for producing such circuit boards.

A circuit board according to an example embodiment of the present invention includes an insulating layer including a first main surface and a second main surface facing each other in a thickness direction, a first conductor layer on the first main surface of the insulating layer, a second conductor layer on the second main surface of the insulating layer, an interlayer connection conductor penetrating the insulating layer in the thickness direction and connected to the first conductor layer and the second conductor layer, and a rustproof layer on a surface of the first conductor layer or the second conductor layer. The interlayer connection conductor includes a first portion including a single metal and a second portion including at least a metal different from the first portion in the thickness direction. The first portion is bonded to the second portion with a first intermediate layer interposed therebetween, the first intermediate layer including the metal included in the first portion and the metal included in the second portion, and bonded to the first conductor layer without the first intermediate layer interposed therebetween. The second portion is bonded to the second conductor layer with a second intermediate layer interposed therebetween, the second intermediate layer including the metal included in the second portion and a metal included in the second conductor layer. The rustproof layer is provided at least at the interface between the first conductor layer and the insulating layer, and is not provided between the second portion and the second conductor layer.

A method for producing a circuit board according to an example embodiment of the present invention includes preparing a base in which a conductor layer is formed on one surface of an insulating layer and a rustproof layer is provided on at least a surface of the conductor layer on the insulating layer side, forming a via hole penetrating the insulating layer and exposing a portion of an upper surface of the conductor layer in the base, removing the rustproof layer in an exposed portion of the conductor layer, filling the via hole from which the rustproof layer has been removed with a first material made of a single metal, and then with a second material including at least a metal different from the first material, and stacking a plurality of bases including the base filled with the first material and the second material, and collectively pressing the stacked bases by applying heat and pressure.

According to example embodiments of the present invention, it is possible to provide circuit boards each with excellent connection reliability between an interlayer connection conductor and a conductor layer, and methods for producing such circuit boards.

The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the example embodiments with reference to the attached drawings.

Example embodiments of the present invention will be described in detail below with reference to the drawings.

Hereinafter, circuit boards and methods for producing circuit boards according to example embodiments of the present invention will be described.

However, the present invention is not limited to the following configurations, and changes can be appropriately applied thereto within a range not changing the scope of the present invention. The present invention also includes a combination of two or more of the individual preferred configurations of the present invention described below.

In the present specification, the term (for example, “vertical”, “parallel”, “orthogonal”, and the like) indicating the relationship between elements and the term indicating the shape of an element are not expressions indicating only a strict meaning, but are expressions meaning to include a substantially equivalent range, for example, a difference of about several %. In addition, in the present specification, “equivalent” is not an expression meaning only a case of being completely equivalent, but is an expression meaning that a case of being substantially equivalent includes, for example, a difference of about several %.

The drawings illustrated below are schematic views, and dimensions, scales of aspect ratios, and the like may be different from those of actual products. In the drawings, the same or corresponding portions are denoted by the same reference numerals. In each drawing, the same elements are denoted by the same reference numerals, and redundant description will be omitted.

1 FIG. 2 FIG. 1 FIG. is a perspective view schematically illustrating an example of a circuit board according to an example embodiment of the present invention.is a cross-sectional view of the circuit board illustrated intaken along line II-II.

1 100 110 120 130 140 150 160 170 180 185 100 190 195 200 210 1 FIG. A circuit boardillustrated inincludes an insulating baseformed by stacking insulating layers (first insulating layer, second insulating layer, third insulating layer, and fourth insulating layer), a conductor layer (mounting electrode, ground line, signal line, line, line) provided on or inside the insulating base, an interlayer connection conductor, an interlayer connection conductor, an interlayer connection conductor, and a protective layer, for example.

1 FIG. 1 In the example illustrated in, the circuit boardis a multilayer circuit board including a plurality of insulating layers.

1 1 The circuit boardmay be a rigid board or a flexible board. The circuit boardmay include a bent portion.

2 FIG. 2 FIG. 100 150 180 210 100 160 170 185 110 120 120 130 On one main surface (lower surface in) of the insulating base, the mounting electrode, the line, and the protective layerare provided. On the other main surface (upper surface in) of the insulating base, the ground lineis provided. The signal lineand the lineare provided between the first insulating layerand the second insulating layerand between the second insulating layerand the third insulating layer.

190 200 110 120 190 170 170 190 110 190 120 170 150 190 110 2 FIG. The interlayer connection conductorsandare provided inside the first insulating layerand the second insulating layer. Among them, the interlayer connection conductorsconnected to the signal lineoverlap in the stacking direction (Z direction in). Therefore, the signal linesare connected by the interlayer connection conductorprovided inside the first insulating layerand the interlayer connection conductorprovided inside the second insulating layerto define a transmission line. Further, the signal lineis connected to the mounting electrodeby an interlayer connection conductorprovided inside the first insulating layer.

195 130 140 Interlayer connection conductorsare provided inside the third insulating layerand the fourth insulating layer.

160 180 200 110 200 120 195 130 195 140 The ground lineis connected to the lineby the interlayer connection conductorprovided inside the first insulating layer, the interlayer connection conductorprovided inside the second insulating layer, the interlayer connection conductorprovided inside the third insulating layer, and the interlayer connection conductorprovided inside the fourth insulating layer.

185 200 110 200 120 200 120 195 130 The lineis provided between each of the interlayer connection conductorprovided inside the first insulating layerand the interlayer connection conductorprovided inside the second insulating layer, and between the interlayer connection conductorprovided inside the second insulating layerand the interlayer connection conductorprovided inside the third insulating layer.

195 130 195 140 200 195 200 Although no line is provided between the interlayer connection conductorprovided inside the third insulating layerand the interlayer connection conductorprovided inside the fourth insulating layer, a line may be provided between them. In addition, a line may be provided between the interlayer connection conductorsand between the interlayer connection conductorand the interlayer connection conductor, or no line may be provided between them.

210 210 100 The protective layeris, for example, a coverlay or a resist layer. The protective layermay be provided on both main surfaces of the insulating base, or may be provided on one of the main surfaces.

1 190 170 The circuit boardincludes at least one interlayer connection conductor described in each example embodiment of the present invention described below. For example, an interlayer connection conductor described in each example embodiment described below is preferably included as the interlayer connection conductorconnected to the signal line.

Each example embodiment illustrated below is an example, and partial replacement or combination of configurations illustrated in different example embodiments is possible. In the second and subsequent example embodiments, descriptions of matters common to the first example embodiment will be omitted, and only differences will be described. In particular, the same operation and advantageous effects by the same configuration will not be sequentially described for each example embodiment.

3 FIG. is a cross-sectional view schematically illustrating an example of a circuit board according to a first example embodiment of the present invention.

3 FIG. 3 FIG. 1 10 10 10 21 10 10 22 10 10 30 10 21 22 40 21 22 a b a b Although an overall configuration is not illustrated in, a circuit boardA includes an insulating layerincluding a first main surfaceand a second main surfacefacing each other in a thickness direction (vertical direction in), a first conductor layerprovided on the first main surfaceof the insulating layer, a second conductor layerprovided on the second main surfaceof the insulating layer, an interlayer connection conductorprovided to penetrate the insulating layerin the thickness direction and connected to the first conductor layerand the second conductor layer, and a rustproof layerprovided on a surface of the first conductor layeror the second conductor layer.

10 21 22 10 The insulating layeris, for example, a resin insulating layer including a resin as a main component. In a case where the first conductor layeror the second conductor layeris a signal line, a resin having a low dielectric constant is included in the insulating layer, so that loss at the time of signal transmission can be reduced.

10 21 22 10 Alternatively, the insulating layermay be a ceramic insulating layer including ceramic as a main component. When the first conductor layeror the second conductor layeris an antenna electrode, a ceramic having a high dielectric constant is included in the insulating layer, so that radiation or reception can be performed in a wide band.

The resin of the resin insulating layer may be, for example, a thermosetting resin or a thermoplastic resin, but is preferably a thermoplastic resin. In a case where the resin insulating layer is made of a thermoplastic resin, a plurality of resin sheets on which the conductor layer is provided can be stacked, and collectively press-bonded (collectively pressed) by heat treatment.

Examples of the thermosetting resin include an epoxy resin, a phenol resin, a polyimide resin or a modified resin thereof, or an acrylic resin.

Examples of the thermoplastic resin include a liquid crystal polymer (LCP), a fluororesin, a thermoplastic polyimide resin, a polyether ether ketone resin (PEEK), or a polyphenylene sulfide resin (PPS).

The resin insulating layer is, for example, preferably made of liquid crystal polymer (LCP). Liquid crystal polymers have lower water absorption than other thermoplastic resins. Therefore, when the resin insulating layer is made of a liquid crystal polymer, moisture remaining in the resin insulating layer can be reduced.

The resin insulating layer may include an inorganic material such as a ceramic filler, for example.

Examples of the ceramic filler include boron nitride, talc, or fused silica.

Examples of the ceramic of the ceramic insulating layer include a low-temperature co-fired ceramic (LTCC) or a high-temperature co-fired ceramic (HTCC).

10 The thickness of one layer of the insulating layeris, for example, preferably about 10 μm or more and about 100 μm or less.

21 22 21 22 Each of the first conductor layerand the second conductor layermay have a patterned shape obtained by patterning the layer into lines, for example, or may have a planar shape spread over one surface. The shapes of the first conductor layerand the second conductor layermay be the same as or different from each other.

21 22 21 22 21 22 Each of the first conductor layerand the second conductor layeris, for example, a metal layer including at least one of copper, silver, aluminum, stainless steel, nickel, gold, or these metals. The materials of the first conductor layerand the second conductor layermay be the same as or different from each other. Both of the first conductor layerand the second conductor layerare, for example, preferably made of a metal foil, and more preferably made of a copper (Cu) foil.

21 22 Each of the first conductor layerand the second conductor layermay have a mat surface on one main surface and a shiny surface on the other main surface.

21 22 21 22 The thickness (length in the stacking direction) of each of the first conductor layerand the second conductor layeris, for example, preferably about 1 μm or more and about 35 μm or less, and more preferably about 6 μm or more and about 18 μm or less. The thickness of the first conductor layerand the second conductor layermay be the same as or different from each other.

21 22 The first conductor layerand the second conductor layermay or may not be parallel or substantially parallel to each other.

10 21 22 10 10 21 22 10 10 21 22 10 One insulating layermay be provided between the first conductor layerand the second conductor layer, or two or more insulating layersmay be provided. When two or more insulating layersare provided between the first conductor layerand the second conductor layer, the configurations of the insulating layersmay be the same as or different from each other. In addition, when two or more insulating layersare provided between the first conductor layerand the second conductor layer, the thickness of the insulating layersmay be the same as or different from each other.

30 21 22 10 21 22 30 10 21 22 The interlayer connection conductoris provided so as to be connected to the first conductor layerand the second conductor layerwhile penetrating the insulating layerin the thickness direction but not penetrating the first conductor layerand the second conductor layer. Therefore, the interlayer connection conductorpenetrates the insulating layer(s)in the thickness direction by the number of layers provided between the first conductor layerand the second conductor layer.

30 In a cross section perpendicular or substantially perpendicular to the thickness direction, preferably the shape of the interlayer connection conductoris circular. In this case, not only a perfect circle but also an ellipse, an oval, and the like are included in the circle.

30 31 32 The interlayer connection conductorincludes a first portionand a second portionin the thickness direction.

31 The first portionincludes a single metal.

31 The first portionis, for example, a plated via. Here, the plating via means a film grown by a liquid phase method or a gas phase method, for example.

31 31 21 When the first portionis a plated via, the metal included in the first portionis preferably the same as the metal of the first conductor layer, and is, for example, Cu.

32 31 The second portionincludes at least a metal different from that of the first portion.

32 1 32 31 22 The second portionis, for example, a paste via. Here, the paste via means a solidified paste. When the circuit boardA is manufactured by collective pressing described later, the second portiondefines and functions as a bonding material, so that the first portionand the second conductor layercan be conductively connected.

32 32 32 31 32 When the second portionis a paste via, examples of the metal included in the second portioninclude Cu, Sn, Ag, Ni, Cr, Pt, Mo, Ga, Ge, Sb, In, Pb, or an alloy including at least one of these metals. The metal included in the second portionmay be the same as or different from the metal included in the first portion. The metal included in the second portionis, for example, an alloy including Cu and Sn.

32 Alternatively, the second portionmay be a plated via.

32 32 32 When the second portionis a plated via, examples of the metal included in the second portioninclude Sn. By using Sn having a low melting point, it is easy to cause the second portionto define and function as a bonding material.

31 32 51 51 31 32 21 51 The first portionis bonded to the second portionwith a first intermediate layerinterposed therebetween, the first intermediate layerincluding the metal included in the first portionand the metal included in the second portion, and bonded to the first conductor layerwithout the first intermediate layerinterposed therebetween.

32 51 31 51 51 32 3 5 As an example, in the second portion, the first intermediate layerincluding Cu and Sn is provided at the end portion on the first portionside. In this example, the first intermediate layeris made of a Cu—Sn alloy such as CuSn or CuSn. However, the composition of the first intermediate layeris different from the composition of the second portion.

31 21 31 21 31 21 The first portionand the first conductor layerare directly bonded without interposing a dissimilar material therebetween. Therefore, at the interface between the first portionand the first conductor layer, there is a portion where different materials do not exist, that is, a portion where the first portionand the first conductor layerare in direct contact with each other.

32 22 52 52 32 22 The second portionis bonded to the second conductor layerwith a second intermediate layerinterposed therebetween, the second intermediate layerincluding the metal included in the second portionand the metal included in the second conductor layer.

32 52 22 52 52 32 3 5 As an example, in the second portion, the second intermediate layerincluding Cu and Sn is provided at the end portion on the second conductor layerside. In this example, the second intermediate layeris made of a Cu—Sn alloy such as CuSn or CuSn. However, the composition of the second intermediate layeris different from the composition of the second portion.

3 FIG. 52 22 10 52 22 10 In the example illustrated in, the second intermediate layerextends to the interface between the second conductor layerand the insulating layer, but as described later, the second intermediate layermay not extend to the interface between the second conductor layerand the insulating layer.

51 52 The first intermediate layermay include one layer or two or more layers. Similarly, the second intermediate layermay include one layer or two or more layers.

51 52 10 51 52 31 32 31 32 The first intermediate layerand the second intermediate layercan be confirmed, for example, by observing a cross section of the insulating layercut in a direction parallel or substantially parallel to the thickness direction using a scanning electron microscope (SEM). Since the first intermediate layerand the second intermediate layerare different in composition from both of the first portionand the second portion, it is displayed in a color tone different from those of the first portionand the second portionin the SEM photograph.

5 3 6 5 Even when the types of included metal elements are the same, the case where the content ratios of the respective metal elements are different is also considered as being “different in composition”. For example, it can be said that the compositions of CuSn, CuSn, CuSn, or the like are all compositions including Cu and Sn as metal species, but the compositions are different from each other because the content ratios of the metal species are different.

40 The rustproof layeris formed by, for example, subjecting the surface of the metal foil to a rustproof treatment using a metal such as Zn, Ni, Cr, Mo, or Pt.

40 21 10 32 22 The rustproof layeris disposed at least at the interface between the first conductor layerand the insulating layer, and is not disposed between the second portionand the second conductor layer.

1 40 21 10 21 21 10 When the circuit boardA is produced by collective pressing described later, for example, the rustproof layeris disposed at the interface between the first conductor layerand the insulating layerto prevent oxidation of the metal foil such as the Cu foil of the first conductor layer, so that it is possible to reduce or prevent a decrease in adhesion between the first conductor layerand the insulating layer.

1 21 10 22 10 40 21 10 When the circuit boardA is manufactured by collective pressing, the thermal load applied to the interface between the first conductor layerand the insulating layeris greater than that applied to the interface between the second conductor layerand the insulating layer. Therefore, preferably, the rustproof layeris disposed at least at the interface between the first conductor layerand the insulating layer.

40 32 22 32 22 40 52 40 32 22 52 30 22 On the other hand, when the rustproof layeris disposed between the second portionand the second conductor layer, a reaction between a material (for example, conductive paste) of the second portionand a material (for example, metal foil) of the second conductor layeris reduced or prevented by rustproof layer, and the second intermediate layeris hardly formed. Therefore, by not disposing the rustproof layerbetween the second portionand the second conductor layer, the second intermediate layeris easily formed, so that the connection reliability between the interlayer connection conductorand the second conductor layercan be improved.

1 40 22 10 32 22 3 FIG. In the circuit boardA illustrated in, the rustproof layeris not disposed at the interface between the second conductor layerand the insulating layer. This makes it possible to prevent inhibition of a reaction between a material (for example, conductive paste) of the second portionand a material (for example, metal foil) of the second conductor layer.

40 21 10 31 31 The rustproof layerdisposed at the interface between the first conductor layerand the insulating layermay be in contact with the first portionor may not be in contact with the first portion.

3 FIG. 40 31 21 31 21 51 30 21 As illustrated in, preferably, the rustproof layeris not disposed between the first portionand the first conductor layer. As described above, the first portionis bonded to the first conductor layerwithout the first intermediate layerinterposed therebetween. As a result, the connection strength between the interlayer connection conductorand the first conductor layercan be increased.

30 3 FIG. The shape of the interlayer connection conductoris not limited to.

32 21 22 52 32 22 32 22 32 22 The second portionmay have a tapered shape in which the area of the end surface on the first conductor layerside is smaller than the area of the end surface on the second conductor layerside. Although the fragile second intermediate layermay be provided at the end portion of the second portionon the second conductor layerside, the connection strength between the second portionand the second conductor layercan be increased by increasing the area of the second portionat the portion connected to the second conductor layer.

31 21 22 Further, the first portionmay have a tapered shape in which the area of the end surface on the first conductor layerside is smaller than the area of the end surface on the second conductor layerside.

3 FIG. 30 21 22 Therefore, as illustrated in, the interlayer connection conductormay have a tapered shape in which the area of the end surface on the first conductor layerside is smaller than the area of the end surface on the second conductor layerside.

30 31 32 32 32 30 31 32 31 32 30 1 2 2 1 2 2 1 2 1 2 When the interlayer connection conductorhas a tapered shape, the height tof the first portionmay be equal or substantially equal to the height tof the second portion, may be less than the height tof the second portion(t<t), but is preferably greater than the height tof the second portion(t>t). When the interlayer connection conductorhas a tapered shape, the connection area between the first portionand the second portionis increased by making the height tof the first portiongreater than the height tof the second portion, so that the connection reliability of the interlayer connection conductorcan be improved.

3 FIG. 31 22 22 21 In the example illustrated in, the end surface of the first portionon the second conductor layerside is flat. However, as described later, the end surface may protrude toward the second conductor layeror may be recessed toward the first conductor layer.

1 The circuit boardA is produced, for example, by the following method.

4 4 FIGS.A toG 1 1 1 are cross-sectional views schematically illustrating an example of a method for producing a circuit boardA. The circuit boardA may be manufactured in a state of one chip (individual piece), or may be manufactured by manufacturing a collective board and then separating the collective board into individual pieces. The collective board here refers to a board including a plurality of circuit boardsA.

4 FIG.A 60 20 10 40 20 10 First, as illustrated in, a baseis prepared in which the conductor layeris formed on one surface of the insulating layer, and the rustproof layeris provided on at least a surface of the conductor layeron the insulating layerside.

10 20 10 For example, a metal foil such as a Cu foil is laminated on one main surface of the insulating layer, and the metal foil is patterned by photolithography to form the conductor layer. The insulating layeris, for example, a resin sheet including a thermoplastic resin such as a liquid crystal polymer as a main component.

4 FIG.B 70 10 20 60 70 Next, as illustrated in, a via holepenetrating the insulating layerand exposing a portion of the upper surface of the conductor layeris formed in the base. The via holepreferably has a tapered shape.

70 10 20 For example, the via holeis formed in the insulating layerwith a laser, for example, such that the upper surface of the conductor layeris exposed.

4 FIG.C 40 20 Subsequently, as illustrated in, the rustproof layerprovided on the exposed portion of the conductor layeris removed.

20 70 40 For example, the upper surface of the conductor layerexposed from the via holeis acid-cleaned, and then a soft etching, for example, is performed so that the rustproof layeris removed.

4 4 FIGS.A toC 4 FIG.C 4 FIG.A 20 10 20 20 Although not illustrated in, it is preferable to remove a rustproof layer (not illustrated) provided on a surface of the conductor layeron a side opposite to the insulating layer. For example, the rustproof layers provided on the upper and lower surfaces of the conductor layermay be simultaneously removed at the stage of, or the rustproof layer provided on the lower surface of the conductor layermay be removed at a stage before.

4 FIG.D 70 40 71 70 71 71 10 Then, as illustrated in, the via holefrom which the rustproof layerhas been removed is filled with a first materialincluding a single metal. The via holeis partially filled with the first material. The height of the first materialis not limited as long as it does not exceed the thickness of the insulating layer.

70 40 71 31 71 4 FIG.G For example, the via holefrom which the rustproof layerhas been removed is filled with a plating metal such as Cu as the first materialby a plating process such as an electrolytic plating process. The first portion(see) is formed of the first material.

4 FIG.E 72 71 70 71 70 71 72 Thereafter, as illustrated in, the second materialincluding at least a metal different from the first materialis poured into the via hole, which has been filled with the first material. The space in the via holeis filled with the first materialand the second material.

70 71 72 72 32 4 FIG.G For example, the via holeafter being filled with the first materialis filled with a conductive paste including a metal material such as Cu or Sn and a resin material as the second material. The second materialis solidified by the heating press described later to form the second portion(see).

72 72 71 71 72 70 40 71 72 Although a plating metal such as Sn, for example, can be used as the second material, depending on the metal selected as the second material, there is a risk that the first materialdefining and functioning as the underlying layer will remelt. Therefore, from the viewpoint of improving the degree of freedom of selection of the first materialand the second material, preferably, the via holefrom which the rustproof layerhas been removed is filled with the plating metal as the first material, and then with the conductive paste as the second material.

4 FIG.F 4 FIG.F 60 71 72 60 71 72 60 71 72 As illustrated in, a plurality of bases including the basefilled with the first materialand the second materialare stacked.illustrates an example in which the basefilled with the first materialand the second materialis continuously stacked, but is not limited as long as the basefilled with the first materialand the second materialis included.

4 FIG.G 1 Thereafter, as illustrated in, heat and pressure are applied to press them at once. As a result, the circuit boardA is produced.

1 10 1 According to this example of a producing method, the circuit boardA can be easily manufactured by collectively pressing the insulating layers. Therefore, the manufacturing process of the circuit boardA is reduced, and the manufacturing cost can be reduced.

5 FIG. is a cross-sectional view schematically illustrating an example of a circuit board according to a second example embodiment of the present invention.

1 40 22 10 52 32 22 5 FIG. In the circuit boardB illustrated in, the rustproof layeris disposed at the interface between the second conductor layerand the insulating layerin a range not contacting the second intermediate layer. This makes it possible to prevent inhibition of a reaction between a material (for example, conductive paste) of the second portionand a material (for example, metal foil) of the second conductor layer.

6 FIG. is a cross-sectional view schematically illustrating an example of a circuit board according to a third example embodiment of the present invention.

1 52 22 10 40 22 10 22 10 52 6 FIG. 6 FIG. In the circuit boardC illustrated in, the second intermediate layerdoes not extend to the interface between the second conductor layerand the insulating layer. In, the rustproof layeris not disposed at the interface between the second conductor layerand the insulating layer, but may be disposed at the interface between the second conductor layerand the insulating layerin a range not contacting the second intermediate layer.

7 FIG. is a cross-sectional view schematically illustrating an example of a circuit board according to a fourth example embodiment of the present invention.

1 32 21 22 7 FIG. In the circuit boardD illustrated in, the second portionhas a tapered shape in which the area of the end surface on the first conductor layerside is smaller than the area of the end surface on the second conductor layerside, and the tapered shape has a stepwise varying inclination angle.

1 32 22 1 32 22 7 FIG. 3 FIG. In the circuit boardD illustrated in, the area of the second portionof the portion connected to the second conductor layercan be increased as compared with the circuit boardA illustrated in. Therefore, the connection strength between the second portionand the second conductor layercan be further increased.

7 FIG. In the example illustrated in, the inclination angle of the tapered shape changes in two stages, but may change in three stages or may change in four or more stages.

31 21 22 Further, the first portionmay have a tapered shape in which the area of the end surface on the first conductor layerside is smaller than the area of the end surface on the second conductor layerside. In that case, the taper shape may have different inclination angles in stages.

8 FIG. is a cross-sectional view schematically illustrating an example of a circuit board according to a fifth example embodiment of the present invention.

1 31 22 22 31 22 8 FIG. 8 FIG. In the circuit boardE illustrated in, the end surface of the first portionon the second conductor layerside protrudes toward the second conductor layer. In the example illustrated in, the end surface of the first portionon the second conductor layerside protrudes symmetrically.

9 FIG. is a cross-sectional view schematically illustrating another example of the circuit board according to the fifth example embodiment of the present invention.

1 31 22 22 31 22 9 FIG. 8 FIG. 9 FIG. In the circuit boardF illustrated in, similarly to, the end surface of the first portionon the second conductor layerside protrudes toward the second conductor layer. On the other hand, in the example illustrated in, the end surface of the first portionon the second conductor layerside protrudes asymmetrically.

8 FIG. 9 FIG. 31 22 22 31 32 31 32 As illustrated inor, when the end surface of the first portionon the second conductor layerside protrudes toward the second conductor layer, the connection area between the first portionand the second portionincreases, so that the connection strength between the first portionand the second portioncan be increased.

1 2 2 1 2 2 1 2 1 2 31 32 32 32 31 32 The height tof the first portionmay be equal or substantially equal to the height tof the second portion, may be less than the height tof the second portion(t<t), but is preferably greater than the height tof the second portion(t>t). The height tof the first portionis defined as the height of the highest portion, and the height tof the second portionis defined as the height of the lowest portion.

8 9 FIGS.and In the examples illustrated in, there is one peak, but there may be two or more peaks. When there are two or more peaks, their sizes, heights, and shapes, for example, may be the same or different.

10 FIG. is a cross-sectional view schematically illustrating an example of a circuit board according to a sixth example embodiment of the present invention.

1 31 22 21 31 22 10 FIG. 10 FIG. In the circuit boardG illustrated in, the end surface of the first portionon the second conductor layerside is recessed toward the first conductor layer. In the example illustrated in, the end surface of the first portionon the second conductor layerside is symmetrically recessed.

11 FIG. is a cross-sectional view schematically illustrating another example of the circuit board according to the sixth example embodiment of the present invention.

1 31 22 21 31 22 11 FIG. 10 FIG. 11 FIG. In the circuit boardH illustrated in, similarly to, the end surface of the first portionon the second conductor layerside is recessed toward the first conductor layer. On the other hand, in the example illustrated in, the end surface of the first portionon the second conductor layerside is asymmetrically recessed.

10 FIG. 11 FIG. 31 22 21 31 32 31 32 As illustrated inor, when the end surface of the first portionon the second conductor layerside is recessed toward the first conductor layer, the connection area between the first portionand the second portionincreases, so that the connection strength between the first portionand the second portioncan be increased.

1 2 2 1 2 2 1 2 1 2 31 32 32 32 31 32 The height tof the first portionmay be equal or substantially equal to the height tof the second portion, may be less than the height tof the second portion(t<t), but is preferably greater than the height tof the second portion(t>t). The height tof the first portionis defined as the height of the lowest portion, and the height tof the second portionis defined as the height of the highest portion.

10 11 FIGS.and In the examples illustrated in, there is one peak of the valley, but there may be two or more peaks of the valley. When there are two or more peaks of the valley, their sizes, depths, and shapes, for example, may be the same or different.

22 21 31 22 A portion protruding toward the second conductor layerand a portion recessed toward the first conductor layermay be mixed on the end surface of the first portionon the second conductor layerside.

12 FIG. is a cross-sectional view schematically illustrating an example of a circuit board according to a seventh example embodiment of the present invention.

1 31 21 21 21 10 12 FIG. In the circuit boardI illustrated in, the end surface of the first portionon the first conductor layerside protrudes to the first conductor layerside from the interface between the first conductor layerand the insulating layer.

12 FIG. 31 21 21 21 10 31 21 31 21 As illustrated in, when the end surface of the first portionon the first conductor layerside protrudes to the first conductor layerside from the interface between the first conductor layerand the insulating layer, the connection area between the first portionand the first conductor layerincreases, so that the connection strength between the first portionand the first conductor layercan be increased.

12 FIG. 31 21 In the example illustrated in, the end surface of the first portionon the first conductor layerside protrudes symmetrically, but may protrude asymmetrically.

12 FIG. In the example illustrated in, there is one peak, but there may be two or more peaks. When there are two or more peaks, their sizes, heights, and shapes, for example, may be the same or different.

13 FIG. is a cross-sectional view schematically illustrating an example of a circuit board according to an eighth example embodiment of the present invention.

1 51 31 10 13 FIG. As in the circuit boardJ illustrated in, the first intermediate layermay extend to the interface between the first portionand the insulating layer.

14 FIG.A 14 FIG.B is a cross-sectional view schematically illustrating another example of the circuit board according to the eighth example embodiment of the present invention.is an example of an SEM photograph showing a cross section of the circuit board according to the eighth example embodiment of the present invention.

1 51 31 10 21 10 31 21 14 FIG.A In the circuit boardK illustrated in, the first intermediate layerextends to the interface between the first portionand the insulating layerand extends to the interface between the first conductor layerand the insulating layer. Accordingly, the connection strength between the first portionand the first conductor layercan be further increased.

15 FIG. is a cross-sectional view schematically illustrating an example of a circuit board according to a ninth example embodiment of the present invention.

1 22 31 22 15 FIG. In the circuit boardL illustrated in, a portion protruding toward the second conductor layerexists in a portion of the end surface of the first portionon the second conductor layerside.

15 FIG. 8 FIG. 9 FIG. 31 22 31 32 31 32 As illustrated in, when there is a portion (hereinafter, also referred to as a protruding portion) protruding from a portion of the end surface of the first portionon the second conductor layerside, the connection area between the first portionand the second portionincreases as inor, so that the connection strength between the first portionand the second portioncan be increased.

31 22 One protruding portion may exist or two or more protruding portions may exist in a portion of the end surface of the first portionon the second conductor layerside. When there are two or more protruding portions, their sizes, heights, and shapes, for example, may be the same or different.

15 The height of the protruding portion is, for example, about 1 μm or more and about 20 μm or less. The shape of the protruding portion is not limited to the shape illustrated in FIG..

The maximum diameter of the protruding portion is, for example, about 1 μm or more and about 10 μm or less. Here, the maximum diameter of the protruding portion refers to a diameter when the cross-sectional shape is circular, and refers to a maximum length passing through the center of the cross-section when the cross-sectional shape is other than circular.

16 FIG. is a cross-sectional view schematically illustrating an example of a circuit board according to a tenth example embodiment of the present invention.

1 21 31 22 16 FIG. In the circuit boardM illustrated in, a portion recessed toward the first conductor layerexists in a portion of the end surface of the first portionon the second conductor layerside.

16 FIG. 10 FIG. 11 FIG. 31 22 31 32 31 32 As illustrated in, when there is a portion (hereinafter, also referred to as a recessed portion) recessed from a portion of the end surface of the first portionon the second conductor layerside, the connection area between the first portionand the second portionincreases as inor, so that the connection strength between the first portionand the second portioncan be increased.

31 22 One recessed portion may exist or two or more recessed portions may exist in a portion of the end surface of the first portionon the second conductor layerside. When there are two or more recessed portions, their sizes, depths, and shapes, for example, may be the same or different.

16 FIG. The depth of the recessed portion is, for example, about 1 μm or more and about 20 μm or less. The shape of the recessed portion is not limited to the shape illustrated in.

The maximum diameter of the recessed portion is, for example, about 1 μm or more and about 10 μm or less. Here, the maximum diameter of the recessed portion refers to a diameter when the cross-sectional shape is circular, and refers to a maximum length passing through the center of the cross-section when the cross-sectional shape is other than circular.

31 22 A protruding portion and a recessed portion may be mixed on a portion of the end surface of the first portionon the second conductor layerside.

17 FIG. is a cross-sectional view schematically illustrating another example of the circuit board according to the tenth example embodiment of the present invention.

1 32 21 21 32 51 17 FIG. As in a circuit boardN illustrated in, a portion of the second portionmay be bonded to the first conductor layer. In that case, the first conductor layeris bonded to the second portionwith the first intermediate layerinterposed therebetween.

18 18 18 FIGS.A,B, andC are cross-sectional views schematically illustrating examples of a circuit board according to an eleventh example embodiment of the present invention.

1 1 1 31 31 21 10 21 51 18 FIG.A 18 FIG.B 18 FIG.C 18 FIG.A 18 FIG.B 18 FIG.C As in the circuit boardO illustrated in, the circuit boardP illustrated in, or the circuit boardQ illustrated in, there may be a void inside the first portion. The number, size, and position, for example, of the voids are not limited. For example, the void may exist in the vicinity of the interface between the first portionand the first conductor layeras illustrated in, may exist in the vicinity of the interface between the insulating layerand the first conductor layeras illustrated in, or may exist in the vicinity of the first intermediate layeras illustrated in. In addition to the void or instead of the void, a residue of a resin (carbide) or an oxide of a copper foil (copper oxide) may be present, for example.

19 FIG. is a cross-sectional view schematically illustrating an example of a circuit board according to an eleventh example embodiment of the present invention.

1 21 10 22 10 19 FIG. In the circuit boardR illustrated in, the surface roughness of the portion of the first conductor layerin contact with the insulating layeris greater than the surface roughness of the portion of the second conductor layerin contact with the insulating layer.

19 FIG. 21 10 10 21 21 As illustrated in, by increasing the surface roughness of the first conductor layerat the portion in contact with the insulating layer, the adhesion area between the insulating layerand the first conductor layerincreases, so that the adhesion strength between the two can be increased. Therefore, for example, when an electronic component is mounted on the first conductor layer, the electronic component is hardly peeled off.

20 FIG. is a cross-sectional view schematically illustrating another example of the circuit board according to the eleventh example embodiment of the present invention.

1 21 10 22 10 20 FIG. Also in the circuit boardS illustrated in, the surface roughness of the portion of the first conductor layerin contact with the insulating layeris greater than the surface roughness of the portion of the second conductor layerin contact with the insulating layer.

1 40 21 10 20 FIG. As with the circuit boardS illustrated in, the rustproof layermay not be disposed at the interface between the first conductor layerand the insulating layer.

1 21 10 22 10 21 10 40 21 10 20 FIG. In the circuit boardS illustrated in, the surface roughness of the portion of the first conductor layerin contact with the insulating layeris greater than the surface roughness of the portion of the second conductor layerin contact with the insulating layer, so that the adhesion strength between the first conductor layerand the insulating layercan be increased even if the rustproof layeris not disposed at the interface between the first conductor layerand the insulating layer.

21 FIG. is a cross-sectional view schematically illustrating an example of a circuit board according to a twelfth example embodiment of the present invention.

1 30 21 22 30 21 FIG. In the circuit boardT illustrated in, the interlayer connection conductorhas a shape in which the area of the end surface on the first conductor layerside is equal or substantially equal to the area of the end surface on the second conductor layerside. That is, the interlayer connection conductordoes not have a tapered shape.

31 21 22 32 21 22 Specifically, the first portionhas a shape in which the area of the end surface on the first conductor layerside is equal or substantially equal to the area of the end surface on the second conductor layerside, and the second portionhas a shape in which the area of the end surface on the first conductor layerside is equal or substantially equal to the area of the end surface on the second conductor layerside.

30 1 30 21 30 30 1 30 30 3 FIG. 21 FIG. When the interlayer connection conductorhas a tapered shape as in the circuit boardA illustrated in, strain stress tends to concentrate on a necking portion (in particular, the necking portion between the interlayer connection conductorand the first conductor layer) of the interlayer connection conductor. In contrast, when the interlayer connection conductordoes not have a tapered shape as in the circuit boardT illustrated in, concentration of the strain stress on the necking portion of the interlayer connection conductoris eliminated. Therefore, the stress applied to the interlayer connection conductoris dispersed, so that the connection reliability is improved.

The circuit board of the present invention is not limited to the above example embodiments, and various applications and modifications can be made within the scope of the present invention with respect to the configuration and manufacturing conditions, for example, of the circuit board.

The circuit boards of example embodiments of the present invention are used, for example, as follows.

22 FIG. is a cross-sectional view schematically illustrating an example of a circuit board on which an electronic component is mounted.

22 FIG. 150 2 240 230 220 230 In the example illustrated in, the mounting electrodeof the circuit boardis connected to the external electrodeof the electronic componentvia a conductive bonding materialsuch as solder, for example. Examples of the electronic componentinclude an integrated circuit (IC) and a connector.

23 FIG. is a cross-sectional view schematically illustrating an example of a circuit board having a bent portion.

23 FIG. 3 3 1 3 2 In the example illustrated in, the circuit boardincludes bent portionsPandP. The number and shape, for example, of the bent portions are not limited.

3 3 The insulating layer of the circuit boardis, for example, preferably a resin insulating layer including a thermoplastic resin such as a liquid crystal polymer as a main component. In this case, the circuit boardcan be manufactured by the above-described collective pressing.

Since the circuit board according to example embodiments of the present invention has the configuration described in the above example embodiments, even when the circuit board has a bent portion, rupture suppression against bending stress can be expected.

The following content is disclosed in the present specification.

<1>

A circuit board including an insulating layer including a first main surface and a second main surface facing each other in a thickness direction, a first conductor layer on the first main surface of the insulating layer, a second conductor layer on the second main surface of the insulating layer, an interlayer connection conductor penetrating the insulating layer in the thickness direction and connected to the first conductor layer and the second conductor layer, and a rustproof layer on a surface of the first conductor layer or the second conductor layer, wherein the interlayer connection conductor includes a first portion including a single metal and a second portion including at least a metal different from the first portion in the thickness direction, the first portion is bonded to the second portion with a first intermediate layer interposed therebetween, the first intermediate layer including the metal included in the first portion and the metal included in the second portion, and being bonded to the first conductor layer without the first intermediate layer interposed therebetween, the second portion is bonded to the second conductor layer with a second intermediate layer interposed therebetween, the second intermediate layer including the metal included in the second portion and a metal included in the second conductor layer, and the rustproof layer is provided at least at an interface between the first conductor layer and the insulating layer, and is not provided between the second portion and the second conductor layer.

<2>

The circuit board according to <1>, wherein the rustproof layer is not provided at an interface between the second conductor layer and the insulating layer.

<3>

The circuit board according to <1>, wherein the rustproof layer is provided at an interface between the second conductor layer and the insulating layer in a range not contacting the second intermediate layer.

<4>

The circuit board according to any one of <1> to <3>, wherein the second portion has a tapered shape in which an area of an end surface on the first conductor layer side is smaller than an area of an end surface on the second conductor layer side.

<5>

The circuit board according to <4>, wherein the tapered shape has a stepwise varying inclination angle.

<6>

The circuit board according to any one of <1> to <3>, wherein the interlayer connection conductor has a shape in which an area of an end surface on the first conductor layer side is equal or substantially equal to an area of an end surface on the second conductor layer side, the first portion has a shape in which the area of the end surface on the first conductor layer side is equal or substantially equal to the area of the end surface on the second conductor layer side, and the second portion has a shape in which the area of the end surface on the first conductor layer side is equal or substantially equal to the area of the end surface on the second conductor layer side.

<7>

The circuit board according to any one of <1> to <6>, wherein an end surface of the first portion on the second conductor layer side protrudes toward the second conductor layer or is recessed toward the first conductor layer.

<8>

The circuit board according to any one of <1> to <7>, wherein an end surface of the first portion on the first conductor layer side protrudes to the first conductor layer side from the interface between the first conductor layer and the insulating layer.

<9>

The circuit board according to any one of <1> to <8>, wherein the first intermediate layer extends to an interface between the first portion and the insulating layer.

<10>

The circuit board according to <9>, wherein the first intermediate layer extends to the interface between the first conductor layer and the insulating layer.

<11>

The circuit board according to any one of <1> to <10>, wherein a portion protruding toward the second conductor layer or a portion recessed toward the first conductor layer is provided in a portion of an end surface of the first portion on the second conductor layer side.

<12>

The circuit board according to any one of <1> to <11>, wherein a surface roughness of a portion of the first conductor layer in contact with the insulating layer is greater than a surface roughness of a portion of the second conductor layer in contact with the insulating layer.

<13>

The circuit board according to any one of <1> to <12>, wherein the second intermediate layer extends to an interface between the second conductor layer and the insulating layer.

<14>

The circuit board according to any one of <1> to <13>, wherein the rustproof layer is not provided between the first portion and the first conductor layer.

<15>

The circuit board according to any one of <1> to <14>, wherein the insulating layer includes a resin as a main component.

<16>

The circuit board according to any one of <1> to <14>, wherein the insulating layer includes ceramic as a main component.

<17>

The circuit board according to any one of <1> to <16>, wherein both of the first conductor layer and the second conductor layer includes a metal foil.

<18>

A method for producing a circuit board including preparing a base in which a conductor layer is formed on one surface of an insulating layer and a rustproof layer is provided on at least a surface of the conductor layer on the insulating layer side, forming a via hole penetrating the insulating layer and exposing a portion of an upper surface of the conductor layer in the base, removing the rustproof layer in an exposed portion of the conductor layer, filling the via hole from which the rustproof layer has been removed with a first material made of a single metal, and then with a second material including at least a metal different from the first material, and stacking a plurality of bases including the base filled with the first material and the second material, and collectively pressing the stacked bases by applying heat and pressure.

<19>

The method for producing a circuit board according to <18>, wherein the via hole from which the rustproof layer has been removed is filled with a plating metal as the first material, and is then filled with a conductive paste as the second material.

<20>

The method for producing a circuit board according to <18> or <19>, wherein the insulating layer includes a thermoplastic resin as a main component.

Furthermore, the following content is disclosed in the present specification.

<31>

A circuit board including an insulating layer including a first main surface and a second main surface facing each other in a thickness direction, a first conductor layer on the first main surface of the insulating layer, a second conductor layer on the second main surface of the insulating layer, and an interlayer connection conductor penetrating the insulating layer in the thickness direction and connected to the first conductor layer and the second conductor layer, wherein the interlayer connection conductor includes a first portion including a single metal and a second portion including at least a metal different from the first portion in the thickness direction, the first portion is bonded to the second portion with a first intermediate layer interposed therebetween, the first intermediate layer including the metal included in the first portion and the metal included in the second portion, and being bonded to the first conductor layer without the first intermediate layer interposed therebetween, the second portion is bonded to the second conductor layer with a second intermediate layer interposed therebetween, the second intermediate layer including the metal included in the second portion and a metal included in the second conductor layer, and a surface roughness of the first conductor layer in a portion in contact with the insulating layer is greater than a surface roughness of the second conductor layer in a portion in contact with the insulating layer.

<32>

The circuit board according to <31>, wherein the second portion has a tapered shape in which an area of an end surface on the first conductor layer side is smaller than an area of an end surface on the second conductor layer side.

<33>

The circuit board according to <32>, wherein the tapered shape has a stepwise varying inclination angle.

<34>

The circuit board according to <31>, wherein the interlayer connection conductor has a shape in which an area of an end surface on the first conductor layer side is equal or substantially equal to an area of an end surface on the second conductor layer side, the first portion has a shape in which the area of the end surface on the first conductor layer side is equal or substantially equal to the area of the end surface on the second conductor layer side, and the second portion has a shape in which the area of the end surface on the first conductor layer side is equal or substantially equal to the area of the end surface on the second conductor layer side.

<35>

The circuit board according to any one of <31> to <34>, wherein an end surface of the first portion on the second conductor layer side protrudes toward the second conductor layer or is recessed toward the first conductor layer.

<36>

The circuit board according to any one of <31> to <35>, wherein an end surface of the first portion on the first conductor layer side protrudes to the first conductor layer side from the interface between the first conductor layer and the insulating layer.

<37>

The circuit board according to any one of <31> to <36>, wherein the first intermediate layer extends to an interface between the first portion and the insulating layer.

<38>

The circuit board according to <37>, wherein the first intermediate layer extends to the interface between the first conductor layer and the insulating layer.

<39>

The circuit board according to any one of <31> to <38>, wherein a portion protruding toward the second conductor layer or a portion recessed toward the first conductor layer is provided in a portion of an end surface of the first portion on the second conductor layer side.

<40>

The circuit board according to any one of <31> to <39>, wherein the second intermediate layer extends to an interface between the second conductor layer and the insulating layer.

<41>

The circuit board according to any one of <31> to <40>, wherein the insulating layer includes a resin as a main component.

<42>

The circuit board according to any one of <31> to <40>, wherein the insulating layer includes ceramic as a main component.

<43>

The circuit board according to any one of <31> to <42>, wherein both of the first conductor layer and the second conductor layer include a metal foil.

<44>

The circuit board according to any one of <31> to <43>, further including a rustproof layer on the surface of the first conductor layer or the second conductor layer, wherein the rustproof layer is provided at least at the interface between the first conductor layer and the insulating layer, and is not provided between the second portion and the second conductor layer.

<45>

The circuit board according to <44>, wherein the rustproof layer is not provided at an interface between the second conductor layer and the insulating layer.

<46>

The circuit board according to <44>, wherein the rustproof layer is provided at an interface between the second conductor layer and the insulating layer in a range not contacting the second intermediate layer.

<47>

The circuit board according to any one of <44> to <46>, wherein the rustproof layer is not provided between the first portion and the first conductor layer.

<48>

A method for producing a circuit board including preparing a base in which a conductor layer is formed on one surface of an insulating layer, and the surface roughness of the conductor layer on the insulating layer side is greater than the surface roughness of a side opposite to the insulating layer, forming a via hole penetrating the insulating layer and exposing a portion of an upper surface of the conductor layer in the base, filling the via hole with a first material including a single metal, and then with a second material including at least a metal different from the first material, and stacking a plurality of bases including the base filled with the first material and the second material, and collectively pressing the stacked bases by applying heat and pressure.

<49>

The method for producing a circuit board according to <48>, wherein the via hole is filled with a plating metal as the first material, and is then filled with a conductive paste as the second material.

<50>

The method for producing a circuit board according to <48> or <49>, wherein the insulating layer includes a thermoplastic resin as a main component.

While example embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.